A semiconductor pressure sensor using semiconductor a strain gage has been used for measurement of an intake air pressure in an automobile and others. In recent years, with the aim of improving cleanliness exhaust gas, the adoption of EGR for recirculating exhaust gas to an intake air system has been spread and a recirculation rate of EGR tends to increase particularly in an application to a diesel engine. Since a semiconductor pressure sensor for pressure measurement on the intake air system with EGR has been used in an environment where the semiconductor pressure sensor is more likely to be exposed in exhaust gas, the necessity of resistance to exhaust gas is increasing.
Further, in the case of a diesel engine, the adoption of a DPF (Diesel Particulate Filter) is under way in order to reduce particulate matters (PMs) and there is a need to sense pressures on both of upstream from and downstream from the filter in order to detect clogging of the filter. On this occasion, a pressure sensitive element of a pressure sensor for use the clogging detection is required to have resistance to exhaust gas.
In the case of a conventional semiconductor pressure sensor, as shown in FIG. 3 of Patent Document 1 (JP-A No. 153508/1998), aluminum is generally used for an electrode chip of a semiconductor strain gage. An aluminum electrode is susceptible to corrosion and a measure against the corrosion is necessary when it is used in a corrosive environment.
In Patent Document 1, a Ti coating film and a Pd coating film are used as a measure for preventing the corrosion of the aluminum electrode. Such a measure is particularly aimed at improving corrosion resistance of the aluminum electrode against humidity and moisture. However the measure is still insufficient for the resistance of corrosion caused by nitrate ions in nitrogen oxide contained in exhaust gas.
Patent Document 1: JP-A No. 153508/1998